Questions to drichards regarding the managed code for the multimeter

drichards,

I’m trying to transform the managed code you wrote for the 22-812 multimeter into one that can read data from a PIC device. In VB.NET I’m using the following code to read from that device:


Public Class Form1
    Inherits System.Windows.Forms.Form
    Dim comms_ok As Boolean = False

<Windows Form Designer generated code>

Public Sub rS232Comms1_DataRxEvent(ByVal sender As System.Object, ByVal e As RS232.RxEventArgs) Handles RS232Comms1.DataRxEvent

        Dim LengthOfString As Integer
        Dim buffer() As Byte = e.data
        Dim oEncoder As New System.Text.ASCIIEncoding
        Dim oEnc As System.Text.Encoding = oEncoder.GetEncoding(1252)
        Dim byteValueString As String
        Dim byteValueInteger0 As Double ' This is the value of the first Channel (Channel 0)
        Dim byteValueInteger1 As Double ' This is the value of the second Channel (Channel 1)
        Dim byteValueInteger2 As Double ' This is the value of the third Channel (Channel 2)
        Dim byteValueInteger3 As Double ' This is the value of the fourth Channel (Channel 4)

        Dim millivolts0 As Double
        Dim millivolts1 As Double
        Dim millivolts2 As Double
        Dim millivolts3 As Double

        Dim FirstNumber As Integer
        Dim SecondNumber As Integer
        Dim ThirdNumber As Integer
        Dim FourthNumber As Integer

        TextBox1.Clear()

       
        ‘ This gives the length of the string which is obtained from the port
        LengthOfString = CInt(e.data.Length.ToString)
       
        ‘ This converts the byte sent by the device into an ASCII number – see the Dim’s above – they are instrumental in receiving that byte
        byteValueString = oEnc.GetString(buffer)

 
        ‘ Here the separate four sets of data are extracted from the common string byteValueString
        Try
            FirstNumber = byteValueString.Substring(1, 6)
            SecondNumber = byteValueString.Substring(9, 5)
            ThirdNumber = byteValueString.Substring(15, 6)
            FourthNumber = byteValueString.Substring(22, 6)
        Catch ex As Exception
        Finally
        End Try

        ‘ This is where the above-obtained parts of the string byteValueString are converted into Integer values
        Try
        ‘ This gives the voltage
            byteValueInteger0 = CInt(byteValueString.Substring(1, 6))

            millivolts0 = (CInt(byteValueInteger0) / 1023) * 5
            millivolts0 = (Int(millivolts0 * 1000)) / 1000
            TextBox1.AppendText("     " & CStr(millivolts0) & "  V" & "  " & Chr(13) & Chr(10))

            byteValueInteger1 = CInt(SecondNumber)

            millivolts1 = (CInt(byteValueInteger1) / 1023) * 5
            millivolts1 = (Int(millivolts1 * 1000)) / 1000
            TextBox1.AppendText("     " & CStr(millivolts1) & "  V" & "  " & Chr(13) & Chr(10))

            byteValueInteger2 = CInt(ThirdNumber) '      

            millivolts2 = (CInt(byteValueInteger2) / 1023) * 5
            millivolts2 = (Int(millivolts2 * 1000)) / 1000
            TextBox1.AppendText("     " & CStr(millivolts2) & "  V" & "  " & Chr(13) & Chr(10))

            byteValueInteger3 = CInt(FourthNumber)

            millivolts3 = (CInt(byteValueInteger3) / 1023) * 5
            millivolts3 = (Int(millivolts3 * 1000)) / 1000
            TextBox1.AppendText("     " & CStr(millivolts3) & "  V")

        Catch ex As Exception
        Finally

        End Try

    End Sub


    '             THE END
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        'If comms_ok Then
        RS232Comms1.CloseComms()
        TextBox1.Clear()
        TextBox1.AppendText("Cya ...")
        'End If
        Me.Dispose()
    End Sub


End Class


To use the above code one has to add in the toolbox a special item – rs232comms.dll. Also I should mention that my PIC device has the following characteristics:

Baud rate = 2400
Byte size = 7
Parity = No parity
Stop bits = 2

The heart of the above code (aside from installing the rs232comms.dll) are the lines

        Dim buffer() As Byte = e.data
        Dim oEncoder As New System.Text.ASCIIEncoding
        Dim oEnc As System.Text.Encoding = oEncoder.GetEncoding(1252)

which allow the incoming data ‘e.data’ to be stored in the variable ‘buffer’ which later can be converted into a string value byteValueString:  

       byteValueString = oEnc.GetString(buffer)

This byteValueString is exactly what I want to obtain with the managed code in Visual C++ .NET and so far I haven’t been able to.

In the code you wrote, the corresponding numerical value (a real number) to the string byteValueString from the above code is dMeterReading. The whole exercise is to obtain the value of that dMeterReading.

Now, to accomplish the above goal, I can see how you have put all the primitives of the necessary functions in the __gc class MultiMeter in the file MultiMeter.h. The functions themselves you have placed in the accompanying MultiMeter.cpp file and, of course, there is a file parameters.h containing a bunch of definitions.

This is the place where it gets confusing to me. For instance, I don’t understand what the meaning of the definitions:

#define SERIAL_READ_PKT_SIZE 9
#define SERIAL_READ_BUF_SIZE 4 * SERIAL_READ_PKT_SIZE

is and should they be changed for my PIC device?

Further, the most important function, namely MultiMeter::ReadData(), which returns the needed dMeterReading when called, assigns a value to that dMeterReading coming from a function which is specific for the 22-812 multimeter (because it calls MultiMeter::Translate22812(BYTE * bBuf)) and does not seem to have anything to do with a PIC device. The PIC device sends data in one compact byte which only needs to be converted into string and doesn’t need the complicated procedure of translation through the function MultiMeter::Translate22812(BYTE * bBuf).

How is this complication caused by MultiMeter::Translate22812(BYTE * bBuf) to be avoided so that the data from the device be stored in one byte and how is this one byte to be converted into a string? This seems to be the main problem I’m having now.